1. Field of the Invention
The present invention relates to a thin-film magnetic head with a heater in an overcoat multilayer, a head gimbal assembly (HGA) with the thin-film magnetic head and a magnetic disk drive apparatus with the HGA.
2. Description of the Related Art
In a magnetic disk drive apparatus, a thin-film magnetic head writes and reads signals to/from a magnetic disk that is rotated by a spindle motor. The thin-film magnetic head has an inductive write head element and a magnetoresistive (MR) effect read head element formed on a slider substrate fixed at an end portion of an suspension of a HGA. During writing or reading signals, the thin-film magnetic head is driven to a desired position on the magnetic disk by a swingable arm.
When writing or reading signals, the thin-film magnetic head hydrodynamically flies with predetermined magnetic spacing (dMS) on the rotating magnetic disk. While flying on the disk, the thin-film magnetic head writes signals to the magnetic disk using a magnetic field generated from the inductive write head element and reads signals by sensing magnetic fields corresponding to the signals from the magnetic disk through an MR effect element.
With the increasing data storage capacity and density of a magnetic disk drive apparatus in recent years, a track width of the thin-film magnetic head is becoming smaller. When the track width is reduced, the writing and reading performance of this magnetic head element is reduced. In order to avoid this problem, latest magnetic disk drive apparatuses have a tendency to reduce dMS. This takes advantage of the fact that magnetic fields corresponding to signals which reaches the thin-film magnetic head from the magnetic disk increases as dMS decreases. The value of dMS is actually designed to be reduced down to the order of 10 nm.
However, during writing signals, Joule heat from the coil layer within an inductive write head element and heat caused by eddy-current loss from the upper and lower pole layers are generated. This heat produces a TPTP (Thermal Pole Tip Protrusion) phenomenon in which an overcoat layer is expanded by heat and the magnetic head element is protruded toward the magnetic disk surface. In this case, the head end face (Pole Tip Recess (PTR) surface) on the same side of the air bearing surface, which is reached by the edges of these magnetic head elements, swells in a shape which is curved toward the magnetic disk surface. As a result, when the designed value of dMS is very small, the protruding MR effect element may contact the magnetic disk surface and frictional heat produced by the contact may cause the electrical resistance value of the MR effect element to change, producing an abnormal signal (thermal asperity).
To avoid this thermal asperity, methods of providing a heater in the vicinity of the magnetic head element to positively generate a TPTP phenomenon and controlling dMS are developed (e.g., U.S. Pat. No. 5,991,113 and U.S. patent Publications Nos. 2003/99054 and 2003/174430). All these methods cause the heater to generate heat by applying electrical currents, expand the overcoat layer and magnetic head element by this heat and positively bring them closer to the magnetic disk surface. The dMS value is controlled by the amount of the electrical currents.
Here, the thin-film magnetic head provided with such a heater is likely to bring about crashes due to the swelling of the overcoat layer. Actually, when a TPTP phenomenon is positively generated by heat from the heater, the PTR surface of the overcoat layer opposite to the slider substrate in relation of the magnetic head element swells more than the PTR surface in the vicinity of the magnetic head element, and especially the portion of the PTR surface close to the trailing edge is likely to swell most. As a result, despite the fact that dMS which is the distance between the end of the magnetic head element and the magnetic disk surface is secured within a predetermined value, the swelling portion of the PTR surface close to the trailing edge may contact the magnetic disk surface, producing crashes and causing damage to the magnetic disk surface and thin-film magnetic head.
To avoid the crashes, there is a method of further recessing the portion close to the trailing edge of the PTR surface. Furthermore, as another method, for example, Japanese Patent Publication No. 04-366408A discloses a thin-film magnetic head whose PTR surface includes a dent. Through this dent, this thin-film magnetic head prevents the portion close to the trailing edge from swelling more than the PTR surface in the vicinity of the magnetic head element even when heated. This makes it possible to avoid crashes.
However, even if the method of further recessing the portion close to the trailing edge of the PTR surface is used, it is difficult to sufficiently suppress the positively generated swelling of the portion close to the trailing edge, depending on the state in which the heater is heated. Furthermore, the method of manufacturing a thin-film magnetic head described in Japanese Patent Publication No. 04-366408A polishes the magnetic head element under a predetermined heating condition so that the PTR surface becomes flat, or mechanically grinds or etches it to the depth corresponding to the amount of swelling due to thermal expansion. Therefore, according to this manufacturing method, the processed parts are quite minute and the amount of grinding or etching is also a very small quantity, and therefore it is unavoidable to produce a large processing variation. As a result, the swelling shape of the processed PTR surface varies from one head to another, resulting in a problem that it is difficult to stably avoid the crashes. Furthermore, the process such as polishing with quite high accuracy is applied after the entire thin-film magnetic head is formed, which increases manufacturing man-hours considerably. There is also another problem that minute shavings, etc., produced during the process may be stuck to the PTR surface, causing an adverse effect on the head operation.
Moreover, processing the PTR surface alone cannot live up to an expectation for an improvement on a degree of the swelling in the PTR surface per the amount of heat from the heater, that is, thermal efficiency in generating a TPTP phenomenon. Actually, depending on the amount of process and its position, there can be a case where an extra heat is required compared to the surface before the process to realize the shape of the PTR surface having a predetermined amount of swelling. Thus, when the thermal efficiency is not sufficiently good, it is necessary to increase the amount of heat generated by the heater to produce a predetermined TPTP phenomenon. As a result, the amount of heat propagating from the heater to the MR effect element increases, causing a decrease in the reading performance in the MR effect element having high temperature dependency of output.